This book addresses the diversity applications and technical features of remote user authentication systems. It contains detailed different issues in the authentication procedures for users at various remote locations schemes. It covers numerous numbers of attacks which are applicable during either registering into the system or accessing the system. It explains comparative analysis of existing solutions based on authentication using some key features such that identity, text password, bio-metric password, smart card etc. Key Features of this book are Review of Kumari et al.'s scheme, Analysis of Kumari et al.'s scheme, Proposed framework for our newly approach system, Our proposed scheme to overcome weaknesses of Kumari et al.'s scheme, Security analysis of our proposed scheme, Comparison of different schemes respect to various attacks, Execution time duration for different phases into their schemes etc.